Ultrasonic in distance measurement

In summary: Example of bad signal||||...... burst |In summary, the newyorker is looking for help with a problem with ultrasonic distance measurement. He is using a 40kHz ultrasonic transducers in distance measurement for waste container level detection. The problem is that the hot season change the air properties in temperature and humidity, which affects the speed of sound. He is looking for a tutorial on how to handle this problem.
  • #1
newyorker
8
0
Hi tehre, this is my firs post here!

I'm designing a complex system using a 40kHz ultrasonic transducers in distance measurement for waste container level detection.
Now I have a big problem because the hot season change the air properties in temperature and humidity.
Anyone may help me where I can find tutorials on how handles this problem?

Thanks to all,

NB
 
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  • #2
Hello newyorker.Whether there is a problem or not I think depends on the level of accuracy you need.I suggest that the first thing you do is to collect data which shows how the speed varies with atmospheric conditions.Try googling NIST and search their site.
 
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  • #3
I remember reading about Polaroid's development of their ultrasonic module and how if the reflecting surface is not flat and uniform, echos from different parts of the surface can arrive out of phase and the echo won't be detected at all. To prevent that, the ultrasonic transmitter steps quickly through four different frequencies.
 
  • #4
Yes, really a frequency sweep could be a good solution, but my transducer is built in an alluminium metal can, because I need it waterproof since I work for the waste field. My transducer has a very narrow bandwidth, 2 or 3kHz maximum, so I cannot follow this way.
 
  • #5
Thanks for your posts...

But anyone knows where I can find C++ library with specific math functions that take in consideration the influence of temperature and humidity in ultrasonic distance measurement?

NB
 
  • #7
skeptic2 said:
http://www.sengpielaudio.com/calculator-speedsound.htm

How accurate must the detector be?

Not high accurated in truth. I have to measure the percentage of empty level of a waste container, but the temperature and air density when sun shining have a huge variation.

Thank U 4 your post...

NY
 
  • #8
How are you measuring the distance? Are you enabling a counter which counts an oscillator until the echo is detected? Are you using a microcontroller? Would it be possible for the microcontroller to read a temperature indicator and adjust the measured distance based on the temperature?
 
  • #9
I'm measuring a distance in a waste container. need to achieve the distance between the roof (where the device is fixed) and the trash on the bottom. The device is mounted outside the tank, so it's exposed to the atmospherics conditions and all job is done via embedded microcontroller card, and I have a temperature sensor, but not inside the tank.
Actually the measure is temperature compesated, but when the air in the tank raise above 122 °F occours a strange phenomena and the temperature compensation is not enought. I think the influence of air humidity, so the air density, change a lot in my measurement. Since, actually I haven't any RH sensing, I'm looking for a measurement method to prevent this trouble.

... mission impossible?

NY
 
  • #10
Which direction is the error? Does it show the distance to be less than actual or greater than actual when the temperature is over 122 F? If you are counting pulses to measure the distance, could the pulse generator be changing frequency with temperature? According to the link I provided, air pressure has no effect on the speed of sound. Would it be possible to locate everything outside the tank except the transducer?
 
  • #11
Dear skeptic2, thank U 4 your posts...

Unfortunately I haven't any target located outside the tank to use as a fix reference...and a frequency variation is not possible, because the transducer has a very narrow bandwidth (4..5kHz only).

Anyway the problem is the following: when temperature is quite cold (less 100/122 F), the received signal is very good and the target echo signal is very clear. But when temperature rise over 120/122 F the received signal has a big offset, that hide any other and this make difficult to detect the echo signal.

I'm trying to reduce the emitting signal, only when temperature is high, but I haven't reach a good goals yet... :(

NY
 
  • #12
How do you determine the distance from the echo time of the ultrasonic pulse. Are you counting pulses or are you integrating a fixed voltage for that period of time?

I don't understand what you mean by offset in your sentence "...the received signal has a big offset, that hide any other and this make difficult to detect the echo signal." Why are you trying to reduce the emitting signal? (reduce the amplitude or frequency?)
 
  • #13
The distance is determined by counting the time between the echo and beginning of 40kHz emitting busrt, through a derivative function.
Not simple to explain...hmm...I'm trying to reduce the emitting signal, by lowering the voltage amplitude applied to pulse tranformer that generates the 40kHz carrier, because sometimes I receive reverberation echo from the tank walls. But it is only a test.

Regarding the sentenced offset, is related to signal scope sampled to the A/D port of the microcontroller.

Example of good signal
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||||...... burst
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| +
| ++
| + +
|===== ===== echo signalExample of dirty signal
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||||...... burst
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| +
| + +
| ++ +
|++++ +++++
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|=============== echo signal with dc offset for temperature effect
 
  • #14
Thanks. So due to the offset, you may be picking up noise that precedes the arrival of the echo resulting in a measurement of too short a distance?
 
  • #15
Not exactly.
By this posting not possible to load image, and the sketch did not represent the phenomena properly.
Really the noise is summed to the scope as a DC offset, so this hide a part of the echo signal. Since I use a derivative function I can detect the echo signal until the noise is not too much.
So the problem is that with temperature increasing, increase the noise and I cannot well understand which is the physics phenomena that gernerate it, but I have only some ideas, because this happens in the tank only, outside it the target detection is very good.

Physics misteria...
 
  • #16
Would it be possible to locate all the electronics outside the tank and run a cable from the electronics to the ultrasonic transducer inside the tank?
 
  • #17
Another thing that might help is to ramp up the receiver gain with time. That way, when the target is close, the echo doesn't overload the receiver and when the target is far, you get noise immunity during the time you're waiting for the echo.
 

What is ultrasonic technology used for in distance measurement?

Ultrasonic technology is used to measure distance by sending high frequency sound waves and measuring the time it takes for the waves to bounce off a target and return to the sender. This time is then converted into a distance measurement.

How accurate is ultrasonic distance measurement?

The accuracy of ultrasonic distance measurement depends on several factors, such as the quality of the ultrasonic sensor, the environment in which it is being used, and the distance being measured. In general, ultrasonic distance measurement can be accurate within a few millimeters.

What are the advantages of using ultrasonic technology for distance measurement?

Ultrasonic technology offers several advantages for distance measurement, including non-contact measurement, high accuracy, and the ability to measure distances in various environments and surfaces. It is also a cost-effective option compared to other distance measurement technologies.

What are the limitations of using ultrasonic technology for distance measurement?

Ultrasonic technology may not be suitable for measuring distances in highly reflective or absorbent surfaces, as the sound waves may not bounce back accurately. It also has a limited range, typically up to 25 feet, and can be affected by ambient noise.

How is ultrasonic technology used in real-world applications for distance measurement?

Ultrasonic distance measurement is commonly used in industries such as manufacturing, robotics, and transportation for tasks such as object detection, level sensing, and collision avoidance. It is also used in consumer products like parking sensors and home security systems.

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